The invention relates to a sintered brake lining with a cylindrical friction element made from a first sintered material, which has an external cylinder surface and a cylinder height, and with a reinforcing element enclosing the friction element which is disposed on the external cylinder surface and extends across at least approximately the entire cylinder height, and the reinforcing element is made from another sintered material with a metal matrix, a brake block comprising a support plate to which several sintered brake linings are secured and a track-bound vehicle disc brake incorporating at least one brake disc and at least one brake block.
The load placed on disc brakes used in track-bound vehicles is constantly rising. There are numerous reasons for this. On the one hand, speeds are becomingly increasingly high and on the other hand, the carriage weights to be decelerated are increasing or attempts are being made to obtain the same braking action with a smaller number of disc brakes. All of this leads to an extra increase in the energy to be converted, which results in even higher temperatures during the braking process. This is where organically bonded friction linings show their limits and it is for this reason that brake linings made from metal friction materials are being used for high-performance brake discs for track-bound vehicles.
For example, EP 0 106 782 B discloses a disc brake block for use in railway applications, with a rigid back plate, which has a top face and a bottom face, with a fixing clamp which is secured to the bottom face of the back plate, with a flexible, metallic support plate which is secured to the top face of the back plate, with several individual friction elements, which are each mechanically secured to the flexible, metallic support plate so that the individual elements can flex when they make contact with a disc to enable them to make full contact with the brake surface, and each friction element has a brake surface content of less than 12.6 cm2 and a ratio of height to brake surface content of not more than 0.6. The friction material of the friction elements is a sintered, metal material with a base of iron. It is also possible to use several individual containers which are filled with friction material and secured to the top face of the back plate.
This arrangement of several friction elements instead of a single friction block has proved to be of particular advantage, especially in terms of functionality under extreme loads and in terms of the performance which can be achieved under wet conditions. The ways in which they are mounted on the support plate range from welding on the friction elements via constructions, whereby the elements are retained by means of intermediate plates, to fitting the friction elements by means of high-temperature soldering processes.
However, the intrinsic strength of friction elements produced in this manner is not sufficient to withstand the high loads which occur during use. One possible way of achieving it is to use casings made from steel plates in the form of rings or pots, as described in the EP-A specification. However, the disadvantage of this is the fact that these plates crease during the braking process, causing wear as a result. This then leads to a change in friction behavior and damages the brake disc.
Another known option is to use so-called reinforcing rings, as described in DE 41 11 926 A. This DE-A describes a multi-element sintered brake lining for partial linings of brake discs for track-bound vehicles in particular, comprising a single or multi-part support plate on the front face of which, facing the friction surface of the brake disc, cylindrical sintered elements are disposed and on the rear face of which a dovetail is provided for securing the brake lining in the brake shoe holder, and the cylindrical sintered elements are each provided with a reinforcing ring which is fixedly connected to the support plate and/or to the sintered element and the height of which extends as far as the wear boundary, and the material of the reinforcing rings has approximately the same wear and friction properties as the sintered elements. The reinforcing ring may also be made from a sintered material, in which case the reinforcing ring can be soldered to or sintered onto the sintered element. To this end, the material of the reinforcing ring is selected so that a coefficient of expansion essentially maintains the shrink fit between the sintered element and reinforcing ring. In order to maintain the shrink fit, it is necessary for both the reinforcing ring and the friction elements to have more or less the same coefficients of expansion. The disadvantage of this is that if wear of the brake lining results in the brake disc touching the reinforcing ring, a change in braking behavior occurs due to the material of the reinforcing ring on the one hand and due to the change, i.e. the increase in available brake surface, on the other hand. Another problem is that this design is restricted to only a few material combinations, due to the fact of having to use identical coefficients of heat expansion as mentioned above. On this subject, DE 93 06 093 U also mentions the fact that strong vibrations occur during operation, which ultimately cause the brake lining described in DE 41 11 926 A to break. Furthermore, fitting brake elements and/or their base plates by welding alone is not enough to achieve the desired strength for the connection of the brake elements to the support plate.
In order to solve this problem, DE 93 06 093 U proposes a brake lining for disc brakes, in particular for high-speed track-bound vehicles, with a single or multi-part support plate, on the front face of which, facing the friction surface of the brake disc, individual brake elements are disposed, and on the rear face of which a fitting or guide is provided for the brake lining, and at least one brake element is connected to a base plate which is in turn connected to the support plate which extends to the side of the brake element and/or is part of a basket enclosing the brake element open towards the front face, and the base plate of the basket of the brake element placed on the support plate is secured to the support plate by means of a first connection and is secured to the support plate at its face remote from the brake element by means of a second connection, and one of the two connections is a welded connection whilst the other connection is a mechanical connection or both connections are welded connections, by which the base plate of the basket placed on the support plate is connected to the support plate at several points of its casing by both press welding and by protective gas welding at its face remote from the brake element.